1. Field of the Invention
This invention relates in general to an apparatus for testing the interface of a slider and rotating disk, and more particularly to a slider-disk interface tester for measuring the friction force at the interface.
2. Description of the Related Art
Slider-disk interface testers, also called “head-disk interface” or HDI testers, are used in the development and manufacturing of magnetic recording disk drives. Such testers typically include a spindle motor with a removable chuck or clamp that allows a magnetic recording disk to be installed, and an actuator with an attached suspension onto which the slider that supports the read/write slider is mounted. The actuator can move the slider in a programmed pattern, which may represent a typical seek pattern during operation of the disk drive, or can maintain the slider over a particular region of the disk. The tester is thus able to simulate the operation of the disk drive and enables various mechanical properties of the interface to be determined, including wear of the slider and disk, fly height of the slider and friction forces. The slider-disk interface testers may use linear or rotary actuators, including rotary voice-coil-motor (VCM) actuators similar to those used in conventional disk drives.
In current disk drive technology, the slider that supports the read/write head is an air-bearing slider that “flies” extremely close, e.g., less than about 10 nm, above the surface of the rotating disk. For future disk drives, the sliders are likely to be in actual contact with the disk surfaces for a significant period of time at high speed, e.g., up to about 100 m/s. Under these conditions, it becomes important to control the friction force acting on the slider and disk to ensure that it is small enough and substantially uniform around the disk so as not to interfere with reading and writing of data. The measurement of friction force at the slider-disk interface is also important for testing various disk and slider materials during disk drive development to ensure that they will have suitable wear properties for disk drive applications, and for measuring the shear forces on thin (e.g., less than about 10 nm) solid overcoat films used on the surfaces of the slider and disk and liquid lubricant films used on the disk surface.
One approach for measuring the friction force has been to use a slider-disk interface tester with an air-bearing slider having a “positive pitch”, with the slider trailing portion in contact with the rotating disk. Positive pitch means that the leading portion of the slider, i.e., the “upstream” portion facing the air flow induced by the rotating disk, is farther from the disk surface than the “downstream ” or trailing portion. However, this approach has the disadvantage that the moment generated by the friction force rotates the trailing portion away from the disk surface, which can momentarily lift the slider off the disk surface. Frequently, this leads to a steady-state-oscillation or “bounce” where the slider continually goes in and out of contact with the rotating disk, making it impossible to reliably measure the friction force during contact. The problem of bounce in contact-recording disk drives has been described by C. M. Mate et al., “Dynamics of Contacting Head-Disk Interfaces”, IEEE Trans. on Magnetics, vol. 40 (2004) pp. 3156–3158.
What is needed is a slider-disk interface tester for use during development and manufacturing of future disk drives and their components that accurately and reliably measures the friction force acting between a slider and rotating disk.